Copolymers of vinyl alcohol (VOH) with a minor amount of 2-acrylamido-2-methyl propane sulfonic acid in free acid form or as a salt of the free acid (AMPS) are known in the art and are useful for various applications, e.g., the production of cold water soluble films which can be formed into containers for predetermined batches of soaps and detergents, temporary sizing for new garments prior to their first washing and oil drilling applications where these copolymers can serve for the temporary shoring up of concrete supports used to maintain the integrity of wells prior to the setting of the concrete.
A problem with the production of these copolymers by prior art methods is that it is difficult to produce the copolymer with a sufficiently high content of polymerized AMPS while maintaining satisfactory levels of productivity and avoiding compositional drift, i.e., unacceptable variations in the content of AMPS in the copolymer from one batch to the next. Thus, any process which is capable of producing VOWAMPS copolymers with satisfactory loading of polymerized AMPS, combined with relatively high productivity and low compositional drift, is much to be desired.
In accordance with this invention, a process is provided for the production of a copolymer of vinyl alcohol (VOH) and 2-acrylamido-2-methyl propane sulfonic acid or a salt of such acid (AMPS) by steps including continuously feeding with agitation, vinyl acetate (VAM) and AMPS as comonomers, a free radical yielding polymerization initiator, and a solvent for said comonomers, initiator, and copolymer resulting from the copolymerization of said comonomers, maintaining the resulting reaction mass in said first reaction zone under polymerization conditions for a residence time sufficient for a major proportion of AMPS fed to said first reaction zone to polymerize, continuously feeding reaction mass from said first reaction zone with an additional supply of AMPS to a second reaction zone, maintaining the reaction mass in the second reaction zone for a residence time sufficient to polymerize a major proportion of the AMPS added to the second reaction zone, continuously withdrawing reaction mass from the second reaction zone, separating copolymer of VAM and AMPS from the latter reaction mass, and saponifying by hydrolysis and/or alcoholyses a major proportion of the acetate groups in said copolymer to form a copolymer of VOH and AMPS.